1. Technical Field
The present invention pertains to retaining wall blocks, methods of manufacturing retaining wall blocks, and methods of assembling retaining walls. More particularly the present invention relates to cast segmental retaining wall blocks, methods of manufacturing cast segmental retaining wall blocks, and methods of assembling retaining walls using the cast segmental retaining wall blocks.
2. Description of the Related Art
Retaining walls are generally made by stacking blocks in a staggered configuration and then filling in the area behind the blocks with a fill material. An upper block is usually stacked on two lower blocks such that the upper block straddles the seam between the two lower blocks. The blocks are typically stacked such that they incorporate a setback, also called a batter, such that the retaining wall has a sloped face. In other words, lower blocks in the retaining wall will project further than upper blocks.
Various methods are used to ensure the mechanical stability of retaining walls. For instance, the blocks typically have protrusions of some kind projecting from their top surfaces, and corresponding depressions in their bottom surfaces. When the blocks are stacked, the protrusions from lower blocks engage with the depressions of upper blocks, thereby providing mechanical stability to the retaining wall. Another method of mechanically stabilizing a retaining wall is to use a stabilizing sheet. The stabilizing sheets are generally placed between upper and lower blocks and extend outward from the back of the retaining wall. In conjunction with the fill material, the stabilizing sheets provide mechanical stability to the retaining wall. According to conventional systems, stabilizing sheets extend across an entire level of blocks (referred to as 100% coverage) and are held in place by metallic rebar rods, plastic tabs, and the like. When used, the metallic rebar rods are generally installed in a side-by-side configuration (i.e. two rods are side-by-side in a single channel in the blocks). Unfortunately, the conventional metallic rebar rods are susceptible to corrosion, which may degrade the mechanical stability over time. Also, the side-by-side configuration of conventional systems allows physical forces from the retaining wall and fill material to act against the rods in such a way that the mechanical stability is weakened. Finally, using 100% coverage of the stabilizing sheets increases the cost of the retaining wall.
It is often desirable for a retaining wall to have some curvature rather than being perfectly flat across their face. The amount of curvature that a block will allow is determined by the design of the block. Specifically, the manner in which the protrusions of lower blocks engage with the depressions of upper blocks in the levels of the retaining wall will limit the amount of curvature allowable in the wall. The angle that side faces of the blocks make with front faces of the blocks will also play a role in the radius of curvature that can be obtained by a specific block design. Conventional block designs may only allow radii of curvature of around 15 feet or more, which may not be suitable for residential landscaping applications.
It is often desirable to provide some type of aesthetically pleasing features on the exposed faces of the blocks in a retaining wall. The features may include color and the faces are typically configured to simulate natural rock features or other aesthetically pleasing patterns.
In order to accomplish the functionality described above, retaining wall blocks are formed by a wet-cast technique in which concrete is poured into forms and allowed to harden, thereby producing a concrete block with the desired characteristics. The blocks are then removed from the forms (referred to as stripping) and may be cured for some amount of time before shipment to customers. Depending on the design of the forms, removing the blocks from the forms may be a multi-step process involving more than one crane lift per block. During the forming process, some type of lilting fixture is usually incorporated into the block in order to facilitate removal from the form and positioning at the site of the retaining wall. The lifting fixture may actually include more than one fixture in the case where more than one crane lift is required to remove the block from the form.
A complete retaining wall system generally includes several types of blocks performing specific functions in the wall. Full blocks are the primary type used and represent the majority of the blocks that will go into a wall. Half blocks are used at the ends of the wall to fill the gaps left by the staggered full blocks. If a retaining wall requires a corner, corner blocks are used at the corner. Finally, top blocks may be utilized in the very top layer of blocks in the retaining wall to give the wall a more aesthetically pleasing appearance. The complete retaining wall system may include any combination of the above-described blocks as will be dictated by the particular retaining wall application.
For several decades ready-mix concrete companies have been using their leftover concrete to cast blocks for storage bins and other forms of retention structures. The blocks were very crude and unsafe to use. In 1982, the LOCK-BLOCK® Retaining Wall System was developed in British Columbia, Canada. The block, which is made with leftover concrete, was configured to be able to build gravity walls and mechanically stabilized earth (MSE) walls. The block fits in a 2.5′×2.5′×5′ envelope, weighs 4,300 lbs, requires 2.4 cubic feet of concrete per square foot of face, has over twenty different shapes, and has three standard facial finishes. 132 sq. ft. of block face is a normal truckload using the LOCK-BLOCK® system. The block does not lend itself to building walls with tight radii, and is too heavy to be used in most residential landscaping applications. The molds used to make this block are heavy and cumbersome to use.
In the late 1980's, a 2′×2′×4′ interlocking block known as the Kelly Block was developed in Fife, Wash. The block weighs 2,200 lbs, requires 2 cubic ft. of concrete per sq. ft. of face area, and typically has a fractured fin face finish. 168 sq. ft. of block face is a normal truckload. The block can be used in both gravity and MSE walls. The block has limited architectural appeal, is difficult to use in radius walls, and has a form that is difficult to set up and strip because of block outs that create the internal holes in the block.
In the early 1990's, a company in Michigan developed a forming and retaining wall system, called REDI-ROCK®. The blocks fit into a 1.5′×3.8′×3.5′ envelope, can weigh up to 2,400 lbs and require up to 2.9 cubic feet of concrete per sq. foot of wall face. 114 sq. ft of block face is a normal truckload. The system was developed to build gravity and MSE walls. The mold system is simple but expensive. The blocks require two hooks for casting, one in the back and one in the top. Removing the block from the mold is a two step process: lifting the blocks straight up out of the mold using the hook on the back, since they are cast face down; laying the block down on its bottom side; and then re-lifting it using the hook on the top for stacking. The blocks can weigh as much as 2,400 lbs and can be used to build walls with a minimum 14.5′ radius of curvature. A few years after the REDI-ROCK® was developed, a similar type of system, called RECON®, except with a different interlocking keyway system, was developed. Although both REDI-ROCK® and RECON® were developed to utilize leftover concrete, due to quality control problems, the blocks are precast using fresh concrete which has substantially increased the price of a block. For example, in Washington State, a REDI-ROCK® block would cost about 65 percent more per sq. ft. than a LOCK BLOCK®.
As described above, conventional retaining wall block systems have several drawbacks including: large envelopes limiting the amount of wall face that can be shipped to a job site in a truck load; low radius of curvature ability; and difficult manufacturing. Further, conventional retaining block forms suffer from several drawbacks including tedious stripping processes and excessive weight.
The present invention addresses these and other disadvantages of the conventional art.